Perhaps you should try some spelling variations:
"international airports economics series" » "international airport economics series", "international transport economics series", "international airshow economics series", "international airports economic series", "international sports economic series"
"international power economy series" » "international poverty economy series", "international ports economy series", "international panel economy series", "international power economic series", "international poor economy series", "international war economy series"

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("international power economy series") or ("international airports economics series"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("international power economy series") OR ("international airports economics series")).
• Removing quotes may allow a broader search: (( international power economy series ) or ( international airports economics series )).
• Adding a wildcard symbol may retrieve word variants: (("international power economy series") or ("international airports economics series"))*.